When an offset press is operated to print, foreign matter such as dust and paper dust tends to adhere to the rollers of the ink supply system. If so, the printed characters or images become blurred or parts of them fail to be printed. As a result, the print quality deteriorates. Accordingly, it is necessary to clean the outer peripheries of the rollers forming an ink supply passage whenever such a defect is found or at regular intervals of time.
The conventional method of cleaning the outer peripheries of the rollers forming an ink supply passage generally involves the following steps.
(1) First, the operation of either the ink supply roller or the ink pump is stopped to cut off the supply of ink.
(2) Then, the cylinders are disengaged from each other, and the inking rollers are moved off the press plates on the plate cylinders.
(3) A scraping doctor blade equipped with a waste liquid recovery tray is pressed against each cylinder.
(4) Each cylinder is rotated while supplying a cleaning solvent into a given portion located in an ink supply passage.
(5) Ink loosened by the solvent, dust and paper dust contained in the ink, and other foreign matter are scraped off by the doctor blade to discharge them into the water liquid recovery portion (see "Newspaper Printing, revised edition", Japan Newspaper Association Corporation, Oct. 31, 1980; left column, line 3-15, p. 209; from line 28 of the left column to line 4 of the right column, page 251. Also see "Offset Press", Japan Printing Newspaper Company, Jun. 25, 1984, lines 10-18, p. 108.)
It is also Known that the aforementioned series of cleaning steps is automated by a sequential control means (see Japanese Patent Publication Nos. 6066/1980 and 24218/1982, Japanese Patent Laid-Open No. 151343/1987.)
When the printing operation ends or the ink color is exchanged, it is necessary to clean the outer peripheries of rollers forming a dampening water supply passage, in addition to the cleaning of the outer peripheries of the rollers forming an ink supply passage. This is done to prevent ink color mixing and to avoid water repellency which would normally be caused by sensitization of a dampening water supply passage.
The prior art method of cleaning the outer peripheries of rollers forming a dampening water supply passage comprises the following steps.
(1) The dampening water application roller is removed from the offset press whenever a given number of sheets are printed or at regular intervals of time.
(2) This roller is cleaned with a known roller cleaner or manually (see the aforementioned "Newspaper Printing, revised edition", lines 19-29, p. 217.)
As described above, the cleaning of an ink supply passage has been already automated, but the cleaning of a dampening water supply passage has relied solely on a worker's manual operation. Further, as the water application rollers are mounted and detached, long time and much labor are needed. Sometimes, the removal and attachment of the rollers are omitted, and the work is done at the mounting position.
Since a dampening water supply passage is frequently mounted at a deep position in a complex portion inside an offset press, the worker is urged to perform a cleaning and wiping operation in a cramped or dangerous posture. In addition, the waste liquid produced by the cleaning flows out, thus fouling the worker's clothes. In this way, the working conditions are inferior. Therefore, the worker becomes physically and mentally unpleasant. Hence, it is highly likely that the working efficiency is low.
Accordingly, when the ink color is changed or the printing operation is complete, the cleaning of the dampening water supply passage tends to be treated lightly and omitted unless the print quality deteriorates too much. If such an omission is repeated, the sensitization of the rollers is promoted. This shortens their life.